Office equipment such as printers and copiers, which place images based on digital data onto sheets, such as sheets of paper are well known. In such equipment it is important that the sheet that is to receive the image is properly aligned with the edge of the feed path as well as not skewed so that the image is properly positioned on the sheet. Various types of registration systems to correct for skew and provide for positioning of the side edge of the sheet are know in the art.
One type of lateral registration system involves the use of two differentially driven nips for deskewing and side registration. Such a system can provide lateral registration of the sheet by deskewing (differentially driving the two nips to remove any sensed initial sheet skew) and then deliberately inducing a fixed amount of sheet skew (rotation) with further differential driving, and driving the sheet forward while so skewed, thereby feeding the sheet sideways as well as forwardly, and then removing that induced skew after providing the desired amount of sheet side-shift providing the desired lateral registration position of the sheet edge.
Another type of system is a translating electronic registration (TELER) system. Such a system generally includes three optical sensors, a pair of coaxial independently driven drive rolls, a carriage with a linear drive on which paper drive rolls are mounted, and a microprocessor controller. A copy sheet is driven into the nip rolls and moved through the paper path for placement and transferring of an image thereon. The speed of both nip rolls can be controlled to effect skew alignment and longitudinal registration. The nip rollers are mounted on a carriage movable transversely with respect to the feed path. A sensor system controls positioning of the carriage to achieve the desired top edge or a lateral positioning of the sheet. Independent control of nip roll drive and carriage translation provides simultaneous alignment in lateral and longitudinal directions.
Examples of these systems may be found in U.S. Pat. No. 4,971,304 to Lofthus; U.S. Pat. No. 5,169,140 to Wenthe, Jr.; U.S. Pat. No. 5,219,159 to Malahowski et al; U.S. Pat. No. 5,278,624 to Kamprath et al; U.S. Pat. No. 5,794,176 to Milillo; U.S. Pat. No. 6,137,989 to Quesnel; U.S. Pat. No. 6,181,153 to Richards et al; U.S. Pat. No. 6,533,268 to Williams et al; U.S. Pat. No. 6,866,260; and U.S. Pat. No. 6,988,725 to Rapkin. The disclosure of each of these patents is incorporated herein by reference in its entirety.
In many of the sheet registration systems, measurement of the lateral (cross process) sheet edge position is required before taking corrective action. For center-registration systems, sheets of varying width (in the cross process direction) require a sensor measurement range of about 60-70 mm for commonly used sheet widths. Previously used sensors such as CCDs become expensive especially when a long array is required. Analog sensors lack the required accuracy.
Other patents showing lateral edge sensors include U.S. Pat. No. 6,373,042 to Kretschmann et al; U.S. Pat. No. 6,511,239 to Kretschmann et al; and U.S. Pat. No. 6,836,627 to Kretschmann et al. The disclosure of each of these patents is incorporated herein by reference in its entirety.
At the present time a moving lateral sensor system is used in a TELER type registration system. A reflective point sensor is attached to a timing belt which is driven by a stepping motor. In the operation, a sensor is positioned in the nominal location before the sheet reaches the registration nips of the registration device which are mounted down stream of the sensor. The nominal sensor location is one-half of the nominal sheet width from the center-line of the paper path. Upon entry of the sheet into the registration device, the lateral registration controller moves the sheet until the lateral sensor detects the sheet edge.
There is a need for an improved type of lateral sensor. In TELER registration devices, the registration controller must move the sheet into positron to be sensed by the sensor in a short period of time. Velocities and accelerations are by necessity large. A sensor as described above is not applicable for use in the two nip differentially driven deskewing system as describe above since in such systems, the position of the sheet must be measured before the registration device starts the registration correction move.